Roller cones having non-integral cutting structures, drill bits including such cones, and methods of forming same

ABSTRACT

Methods of manufacturing roller cones for drill bits include providing both integral teeth and non-integral teeth on the roller cones. A layer of hardfacing may be applied to the integral teeth. Non-integral teeth may be formed on a body of a cone, or they may be separately formed from the body and attached thereto. In some embodiments, the non-integral teeth are formed by building-up the non-integral teeth from hardfacing material. Roller cones and earth-boring tools are formed using such methods.

TECHNICAL FIELD

The present invention relates generally to rotary drill bits for drilling wellbores in subterranean formations, to components of such drill bits, and to methods of manufacturing such drill bits and components.

BACKGROUND

Roller cone earth-boring bits are commonly used for drilling subterranean earth formations. One type of roller cone earth-boring bit is a steel tooth or milled tooth earth-boring drill bit which typically comprises two or more cones with teeth protruding from the surface of each cone for engaging the rock. The teeth are made of hardened steel and generally are triangular in cross-sectional shape (as observed in a plane perpendicular to the rotational axis of the cone). Another type of roller cone earth-boring bit has annular structures exhibiting substantially circular exteriors, which are termed “disks” or “disk cutters,” and protrude from the surface of the cone for engaging the rock. The disks are also made of hardened steel and extend around a circumference of the cone. Surfaces of the milled teeth or disks that engage the rock are usually coated with a layer of hardfacing material to increase wear-resistance. Typical hardfacing material may be formed from a particle-matrix composite material. Such particle-matrix composite materials include particles of hard material such as, for example, tungsten carbide dispersed throughout a metal-matrix material (often referred to as a “binder” material). Particle-matrix composite materials exhibit relatively higher erosion resistance and wear resistance relative to the hardened steel of the teeth and disks.

Deposition of hardfacing material on the surfaces of the milled teeth or disks may be accomplished using manual welding processes or an automated hardfacing system. Typical manual welding processes include a person holding a welding torch and a rod of hardfacing material and welding a coating of hardfacing material to the surface of a tooth. After one tooth has been coated, the person moves the torch, the hardfacing material, and/or the cone to permit the next tooth to be coated. Automated processes may be very complex due to the geometry, inaccessibility to the faces of each tooth or disk by a hardfacing torch, and the number of teeth on a milled-tooth cone.

Whether manual or automatic means are used to apply the hardfacing to the roller cone, the proximity of the teeth and/or disks may make it difficult or impossible to adequately weld hardfacing material to the surfaces of each tooth or disk. As such, there is a need in the art for improved methods of applying hardfacing material to a cone for a roller cone bit.

BRIEF SUMMARY

In some embodiments, the present invention includes methods of forming a roller cone for an earth-boring bit. A non-integral tooth may be formed adjacent at least one integral tooth. For example, a non-integral tooth may be formed in a gap between two-integral teeth. As non-limiting examples, such a gap may be located between at least two integral teeth on different rows of teeth, or such a gap may be located between at least two integral teeth in the same row of teeth.

In additional embodiments, the present invention includes methods of forming a roller cone for an earth-boring rotary drill bit in which at least one non-integral disk cutter is provided on a roller cone adjacent to an integral disk cutter on the cone. For example, a gap may be formed between two integral disk cutters, and at least one non-integral disk cutter may be provided in the gap.

In yet additional embodiments, the present invention includes methods of forming earth-boring rotary drill bits in which a plurality of integral teeth are formed on a cutter, and hardfacing material is deposited on the cutter to form at least one non-integral tooth thereon. For example, the hardfacing material may be deposited on the cutter in a gap between two adjacent integral teeth, and the hardfacing material may be built up to form at least one non-integral tooth between the integral teeth. Furthermore, a hardfacing layer may be applied to at least one surface on each of the adjacent integral teeth.

In further embodiments, the present invention includes methods of forming earth-boring bits in which integral teeth are formed on a cutter, hardfacing is applied to the integral teeth, and a non-integral tooth is separately formed from the cutter and bonded to the cutter in a gap between two integral teeth.

In further embodiments, the present invention includes earth-boring bits having a roller cone mounted to a bit leg. The roller cone includes at least one integral tooth formed on a surface of the roller cone, and at least one non-integral tooth bonded to the surface of the roller cone adjacent the integral tooth.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

While the specification concludes with claims particularly pointing out and distinctly claiming that which is regarded as the present invention, the advantages of this invention may be more readily ascertained from the description of embodiments of the invention when read in conjunction with the accompanying drawings, in which:

FIG. 1 is a perspective view of an embodiment of an earth-boring rotary drill bit of the present invention;

FIG. 2 is an enlarged perspective view of an embodiment of a roller cone of the present invention;

FIG. 3 is an enlarged perspective view of an embodiment of a partially formed roller cone of the present invention;

FIG. 4 is an enlarged perspective view of another embodiment of a partially formed roller cone of the present invention;

FIG. 5 is an enlarged partial view of another embodiment of a partially formed roller cone of the present invention;

FIG. 6 illustrates hardfacing material being applied to the portion of the partially formed roller cone shown in FIG. 5;

FIG. 7 illustrates a cutting structure formed by application of hardfacing material to the portion of the partially formed roller cone, as shown in FIG. 6;

FIG. 8 illustrates an example of a robot that may be used to form roller cones in accordance with embodiments of the present invention;

FIG. 9 is an enlarged partial view of a non-integral tooth being applied to a portion of a partially formed roller cone;

FIG. 10 is a partial cross-sectional view of an embodiment of a roller cone of the present invention that includes a non-integral tooth disposed between two integral teeth of the roller cone;

FIG. 11 is an enlarged partial view of another embodiment of a non-integral tooth applied to a portion of a partially formed roller cone;

FIG. 12 is an enlarged perspective view of another embodiment of a roller cone of the present invention;

FIG. 13 is an enlarged perspective view of another embodiment of a partially formed roller cone of the present invention; and

FIG. 14 is an enlarged perspective view of another embodiment of a partially formed roller cone of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Some of the illustrations presented herein are not meant to be actual views of any particular material, device, or system, but are merely idealized representations which are employed to describe the present invention. Additionally, elements common between figures may retain the same numerical designation.

An embodiment of an earth-boring drill bit 102 of the present invention is illustrated in FIG. 1 as a non-limiting example of a drill bit employing a plurality of roller cones. The drill bit 102 comprises a bit body 104 having three bit legs 106. A cone 109 is rotably mounted to a bearing pin (not shown) on each of the bit legs 106. The cone body 108 (FIG. 2) of each cone 109 may be at least substantially comprised of, for example, an iron-based alloy (e.g., steel). In the embodiment shown in FIG. 1, each cone 109 has three rows of teeth 110, 111 including an outer row 112, an inner row 114, and an intermediate row 116. The cones 109 of the drill bit 102 include both integral teeth and non-integral teeth, as discussed in further detail below.

A circumferential recess 118 may be disposed between the inner row 114 and the intermediate row 116, as well as between the intermediate row 116 and the outer row 112. Each tooth 110 is separated from adjacent teeth in the same row by a valley 128. Each cone 109 also has a gage surface 130 that defines the diameter of the bit and the borehole.

Embodiments of drill bits 102 and cones 109 of the present invention may have any number of rows of teeth 110, 111 and may have any number of teeth 110, 111. Furthermore, embodiments of drill bits 102 and cones 109 of the present invention may have teeth 110, 111 that are arranged in any pattern on the cones 109, and the teeth 110, 111 may not be arranged in rows.

The drill bit 102 has a threaded section 122 at its upper end for connection to a drillstring (not shown). The drill bit 102 also has an internal fluid plenum that extends through the bit body 104, as well as fluid passageways that extend from the fluid plenum to nozzles 124. During drilling, drilling fluid may be pumped down the center of the drillstring, through the fluid plenum and fluid passageways, and out the nozzles 124.

Each bit leg 106 also may include a lubricant reservoir for supplying lubricant to the bearing surfaces between the cones 109 and the bearing pins on which they are mounted. A pressure compensator 126 may be used to equalize the lubricant pressure with the borehole fluid pressure, as known in the art.

FIG. 2 is an enlarged view of a cone 109 of the drill bit 102 shown in FIG. 1. As previously mentioned, the cone 109 includes both integral teeth 110 and non-integral teeth 111. As used herein, the term “integral tooth” means a tooth having at least a major portion thereof that is integrally formed with and an integral part of the cone body 108 of a roller cone 109 such that no identifiable, discrete boundary exists between the cone body 108 of the roller cone 109 and the major portion of the tooth. Such integral teeth 110 may be formed by machining a cone body 108 of a roller cone 109 using machining methods such as, for example, turning, milling, and/or drilling. As used herein, the term “non-integral tooth” means a tooth having a major portion thereof that is either formed separately from and attached to the cone body 108 of a roller cone 109, or is formed on the cone body 108 of the roller cone 109 such that an identifiable discrete boundary exists between the cone body 108 of the roller cone 109 and the major portion of the tooth. In the example embodiment shown in FIG. 2, each of the outer row 112 and the inner row 114 comprises integral teeth 110, while the intermediate row 116 comprises non-integral teeth 111.

At least an outer surface of each tooth 110, 111 of the cone 109 may comprise a hardfacing material 120 (FIGS. 1 and 2). For example, in some embodiments, a layer of hardfacing material 120 may be applied over each integral tooth 110 of the cone 109, and a major portion of each non-integral tooth 111 of the cone 109 may be formed from the hardfacing material 120. In such embodiments, various welding processes including, for example, metal-inert gas (MIG) welding processes, tungsten-inert gas (TIG) welding process, plasma arc welding (PAW) processes may be used to apply a layer of hardfacing material 120 over integral teeth 110 and to form a major portion of non-integral teeth 111 by building up the teeth 111 from the hardfacing material 120 in a layer-by-layer process. Furthermore, the hardfacing material 120 may be applied manually or robotically.

As shown in FIG. 2, the teeth 110, 111 on the cone 109 are formed very close together. If each of the teeth 110, 111 were integrally formed with the cone 109 (i.e., were an integral tooth 110), it might be difficult to apply a layer of hardfacing material 120 over each of the teeth 110, 111 due to the difficulty of positioning a welding torch between the teeth 110, 111. In other words, it may be difficult to appropriately position a welding torch between the teeth 110, 111 to apply hardfacing material 120 to the surfaces thereof due to physical interference between the welding torch and adjacent teeth 110, 111. As a result, the areas of the teeth 110, 111 that could be covered with hardfacing material 120 might be limited. Furthermore, it might be difficult to modify the shape, size, and/or configuration of the teeth 110, 111 on the cone 109 to facilitate such application of hardfacing material 120 without comprising a desirable drilling performance of the drill bit. Additional embodiments of the present invention include methods of forming roller cones for earth-boring roller drill bits that may be used to overcome such problems, as described in further detail herein below.

An example embodiment of a method of the present invention that may be used to form the roller cone 109 shown in FIG. 2 is described below with reference to FIG. 3. A cone body 108 may be machined to form the intermediate cone structure 166 shown in FIG. 3. The intermediate cone structure 166 includes an outer row 112 of integral teeth 110 and an inner row 114 of integral teeth 110. A gap 132 may be formed between the integral teeth 110 of the outer row 112 and the integral teeth 110 of the inner row 114 at the location on the cone body 108 at which non-integral teeth 111 (FIG. 2) will be subsequently formed. The outer row 112 and the inner row 114 of integral teeth 110 may extend circumferentially about a rotational axis of the cone body 108, as shown in FIG. 3.

A layer of hardfacing material 120 (FIG. 5) may be applied to one or more surfaces of each integral tooth 110 of the outer row 112 and the inner row 114. As at least a portion of the hardfacing material 120 is applied to surfaces of the integral teeth 110, the welding torch used to apply the hardfacing material 120 may be at least partially positioned within the gap 132 between the outer row 112 and the inner row 114. By providing the gap 132 between the integral teeth 110 of the outer row 112 and the integral teeth 110 of the inner row 114, physical interference problems may be reduced or eliminated to facilitate the application of the hardfacing material 120 to the integral teeth 110.

After applying a layer of hardfacing material 120 to one or more surfaces of the integral teeth 110, non-integral teeth 111 may be formed on, or separately formed and attached to, the cone body 108 in the gap 132 between the outer row 112 and the inner row 114 to form the cone 109 shown in FIG. 2.

Another embodiment of a method of the present invention that may be used to form a roller cone similar to the roller cone 109 shown in FIG. 2 is described below with reference to FIG. 4. A cone body 108 may be machined to form the intermediate cone structure 170 shown in FIG. 4. The intermediate cone structure 170 includes an outer row 172 of integral teeth 110, an inner row 174 of integral teeth 110, and an intermediate row 176 of integral teeth 110. A gap 182 may be formed between the integral teeth 110 of the outer row 172, between the integral teeth 110 of the inner row 174, and between the integral teeth 110 of the intermediate row 176. The gaps 182 may be located on the cone body 108 at locations at which non-integral teeth 111 (FIG. 2) will be subsequently formed. Each gap 182 may be sized to accommodate one or more non-integral teeth 111.

A layer of hardfacing material 120 (FIG. 2) may be applied to one or more surfaces of each integral tooth 110 of the outer row 172, the inner row 174, and the intermediate row 176. As at least a portion of the hardfacing material 120 is applied to surfaces of the integral teeth 110, the welding torch used to apply the hardfacing material 120 may be at least partially positioned within the gaps 182 between integral teeth 110 in each of the outer row 172, the inner row 174, and the intermediate row 176. By providing the gaps 182 between the integral teeth 110 of the outer row 172, the inner row 174, and the intermediate row 176, physical interference problems may be reduced or eliminated to facilitate the application of the hardfacing material 120 to the integral teeth 110.

After applying a layer of hardfacing material 120 to one or more surfaces of the integral teeth 110, non-integral teeth 111 may be formed on, or separately formed and attached to, the cone body 108 in the gaps 182 between the integral teeth 110 in each of the outer row 172, the inner row 174, and the intermediate row 176 to form a cone similar to the cone 109 shown in FIG. 2.

In additional embodiments of the present invention, intermediate cone structures may be formed to comprise any number of missing teeth and/or rows for subsequently providing non-integral teeth therein. For example, an intermediate cone structure may include both gaps 132 between rows of teeth, as previously described in relation to FIG. 3, as well as gaps 182 between integral teeth 110 in the same row of teeth, as previously described in relation to FIG. 4.

In some embodiments of the present invention, a marking feature or structure may be provided on a cone body 108 of an intermediate cone structure at each location at which a non-integral tooth 111 is to be formed on the cone body 108 or attached to the cone body 108. FIG. 5 is an enlarged partial view of an embodiment of an intermediate cone structure of the present invention, similar to that shown in FIG. 4, and illustrates a marking feature comprising a marking stub 134 formed on the cone body 108 in a gap 182 adjacent an integral tooth 110. The marking stub 134 defines an area on the surface of the cone body 108 in the at least one gap 132 at which a non-integral tooth 111 is to be formed or attached. As shown in FIG. 5, the marking stub 134 may comprise a relatively small protrusion formed on the cone body 108 having a size at least substantially corresponding to a size of a base of a non-integral tooth 111 to be formed on or attached to the marking stub 134. The marking stub 134 may extend, for example, about ⅛ of an inch from a surrounding outer surface of the cone body 108.

In additional embodiments, a cone body 108 may be etched or inscribed to mark the location of non-integral teeth 111 to be formed on or attached to the cone body 108. For example, if a row of non-integral teeth 111 is to be provided on a cone body, as shown in FIG. 3, lines may be etched or inscribed on the cone body 108 that extend circumferentially around the cone body 108 about a rotational axis of the cone body 108 to define longitudinal boundaries of non-integral teeth 111 to be formed on or attached to the cone body 108, and lines may be etched or inscribed on the cone body 108 that extend longitudinally between the circumferential lines to define the circumferential boundaries of non-integral teeth 111 to be formed on or attached to the cone body 108. Such markings may be formed during the machining process or processes used to form the integral teeth 110 on the cone body 108.

As previously mentioned, in some embodiments of the present invention, one or more non-integral teeth 111 may be formed on a cone body 108 by depositing hardfacing material 120 on the cone body 108 in such a manner as to build up the non-integral teeth 111 on the cone body 108 from the hardfacing material 120. FIGS. 6 and 7 illustrate one example of an embodiment of a method of the present invention that may be used to form a non-integral tooth 111 on a cone body 108. Referring to FIG. 6, hardfacing material 120 may be deposited on the cone body 108 (e.g., on a marking stub 134 of a cone body 108 in a gap 132 or a gap 182) in a layer-by-layer process (i.e., successively deposited layers of hardfacing material 120 being deposited over previously deposited layers of hardfacing material 120) so as to form one or more non-integral teeth 111 like that shown in FIG. 7 comprising multiple layers of hardfacing material 120. For example, an integral tooth 110 may be formed on a cone body 108 and a hardfacing material 120 may be applied to a surface of the integral tooth 110. A marking stub 134 may be formed on the cone body 108 adjacent the integral tooth 110, and hardfacing material 120 may be deposited on the marking stub 134 to build up a non-integral tooth 111 on the marking stub 134 from the hardfacing material 120. By way of example and not limitation, the hardfacing material 120 may be deposited by, for example, manually welding the hardfacing material 120 to the cone body 108 using a welding torch 138 and a tube or rod 136 comprising hardfacing material 120. The hardfacing tube or rod 136 and the welding torch 138 may be moved across the surfaces of the integral tooth 110 and the marking stub 134 to weld the hardfacing material 120 to the integral tooth 110 and the marking stub 134. Layers of hardfacing 120 may be sequentially deposited on the marking stub 134 in a layer-by-layer process to form a non-integral tooth 111 having a desirable height and shape.

After forming the non-integral tooth 111 as shown in FIG. 7, surfaces of the non-integral tooth 111 may be machined or ground as necessary or desirable to remove a portion of the hardfacing material 120 to provide the non-integral tooth 111 with a desirable geometry and dimension. In some embodiments, a template structure may be placed over the non-integral tooth 111 and the non-integral tooth 111 may be machined to cause the non-integral tooth 111 to conform to surfaces of the template. Using a template may help to ensure that the non-integral teeth 111 conform to a desirable shape and dimension.

The hardfacing material 120 may have any suitable composite composition comprising a discontinuous hard phase dispersed within a continuous matrix phase. For example, the hardfacing material may comprise relatively hard ceramic particles dispersed throughout a metallic matrix material. Many hardfacing compositions are known in the art and may be employed as a hardfacing material 120 in embodiments of the present invention. Examples of such hardfacing compositions are described in, for example, U.S. Pat. No. 5,663,512, entitled Hardfacing Composition for Earth-Boring Bits, issued Sep. 2, 1997, U.S. Pat. No. 6,248,149, entitled Hardfacing Composition for Earth-Boring Bits using Macrocrystalline Tungsten Carbide and Spherical Cast Tungsten Carbide, issued Jun. 19, 2007, and pending U.S. patent application Ser. No. 11/823,800, entitled Particle-Matrix Composite Drill Bits With Hardfacing and Methods of Manufacturing and Repairing Such Drill Bits Using Hardfacing Materials, filed Oct. 31, 2007, the entire disclosure of each of which document is incorporated herein by this reference.

The hardfacing material 120 may be applied to the cone body 108 using welding techniques. By way of example and not limitation, the hardfacing material 120 may be applied manually using a welding torch and a rod or tube comprising hardfacing material 120. A tube comprising hardfacing material may comprise a hollow, cylindrical tube formed from a metal material that will eventually form a continuous metal-matrix phase of the hardfacing material 120. The tube may be filled with hard particles, such as, for example, tungsten carbide particles that will eventually form a discontinuous hard phase of the hardfacing material 120. At least one end of the hollow, cylindrical tube may be sealed. The sealed end of the tube may then be melted or welded onto the surface of the cone body 108. As the tube melts, the hard particles within the hollow, cylindrical tube mix with and are suspended in the molten matrix material as it is deposited onto the cone body 108. In additional methods, a solid rod of hardfacing material 120 may be used instead of a tube. The welding torch may comprise, for example, an arc welding torch or a fuel torch (e.g., an oxygen-acetylene torch). In yet additional methods, a plasma torch may be used to weld the hardfacing material 120 to the cone body 108. In such methods, powdered hardfacing material 120 (e.g., hard particles and particles comprising metal-matrix material) may be fed through the plasma torch and onto the cone body 108.

In additional embodiments, the hardfacing material 120 may be deposited using an automated (e.g., robotic) process. For example, a welding torch and/or a cone body 108 may be robotically manipulated while using the welding torch to deposit hardfacing material 120 on the cone body 108. Automated welding processes and systems that may be used to deposit the hardfacing material 120 on the cone body 108 are described in, for example, U.S. Pat. No. 5,233,150 entitled Methods of Production of Workpieces by Welding Equipment, filed Aug. 3, 1993, U.S. patent application Ser. No. 10/095,523 entitled Method and Apparatus for Forming a Workpiece, filed Mar. 13, 2002, and U.S. patent application Ser. No. 12/257,219, entitled Method and Apparatus for Automated Application of Hardfacing Material to Drill Bits, filed Oct. 23, 2008, the entire disclosure of each of which document is incorporated herein by this reference.

FIG. 8 illustrates one example of an automated robotic system that may be used to apply hardfacing material 120 to a cone body 108 (e.g., to apply a layer of hardfacing material 120 to surfaces of integral teeth 110 and/or to build-up the non-integral teeth 111 from hardfacing material 140. As shown in FIG. 8, a first robotic device 141A may be used to manipulate a roller cone body 108, and a second robotic device 141B may be used to manipulate a welding torch 138 as the welding torch 138 is used to deposit hardfacing material 120 on the cone body 108. In one embodiment, the cone body 108 may remain stationary while the second robotic device 141B manipulates the welding torch 138 around the surface of the cone body 108. In another embodiment, the welding torch 138 may remain stationary while the first robotic device 141A manipulates the cone body 108 such that the surface of the cone body 108 contacts the welding torch 138. In a further embodiment, both the welding torch 138 and the cone body 108 may be manipulated by the first and second robotic devices 141A and 141B to contact the welding torch 138 with the surface of the cone body 108. A laser sensor 146 may be used to determine a distance between the welding torch 138 and the surface of the cone body 108 and/or to measure a thickness of hardfacing material 120 applied to the surface of the cone body 108. Each of the first and second robotic devices 141A and 141B may be provided with multiple (e.g., five, six, or more) axes of rotation 144 (or degrees of freedom) to provide sufficient freedom of movement between the welding torch 138 and the cone body 108. In some embodiments, the welding torch 138 may comprise a pulsed plasma-transferred arc welding (PTAW) torch in which the torch is used to generate a plasma column between the welding torch 138 and the cone body 108, or a plasma-transferred arc in which the current of the plasma transfer arc may be pulsed as the welding torch 138 is used to deposit hardfacing material 120 on the cone body 108.

In some embodiments, a hardfacing material 120 used to form non-integral teeth 111 may be at least substantially identical in composition to a hardfacing material 120 that is applied over surfaces of integral teeth 110. In additional embodiments, hardfacing material 120 having a first composition may be used to form non-integral teeth 111 on a cone body 108, and hardfacing material 120 having a second, different composition may be used to form a layer of hardfacing material 120 over integral teeth 110 on the cone body 108.

In some embodiments, hardfacing materials 120 having different compositions may be used to form different portions or regions of non-integral teeth 111. For example, an interior region of non-integral teeth 111 may be formed from and comprise hardfacing material 120 having a first composition, and an exterior region of the non-integral teeth 111 may be formed from and comprise a hardfacing material 120 having a second composition differing from that of the first hardfacing material 120. In some embodiments, for example, the composition of the first hardfacing material 120 may exhibit a toughness that is relatively greater than a toughness exhibited by the composition of the second hardfacing material 120, and the composition of the second hardfacing material 120 may exhibit a hardness and/or wear resistance that is relatively greater than a hardness and/or wear resistance exhibited by the composition of the first hardfacing material 120.

As previously mentioned, non-integral teeth 111 may be separately formed from the cone body 108 and subsequently attached thereto. FIG. 9 is an enlarged partial view of a cone body 108 and illustrates a non-integral tooth 111 that is being positioned on and attached to the cone body 108 in a gap 132 adjacent an integral tooth 110. The non-integral tooth 111 may be separately formed from the cone body 108. For example, the non-integral tooth 111 may comprise a particle-matrix composite material (e.g., a hardfacing material) that includes hard particles (e.g., particles of tungsten carbide) dispersed within a metal-matrix material (e.g., a nickel-based, cobalt-based, or iron-based metal alloy).

The non-integral tooth 111 may be formed using, for example, a sintering process in which a particulate green body is sintered to form the non-integral tooth 111. Such a particulate green body may be formed using known green body forming techniques including, for example, powder pressing techniques, powder injection molding techniques, and casting techniques (e.g., slurry casting techniques and tape casting techniques). For example, in an injection molding process, a powder mixture comprising hard particles and particles of a metal-matrix material (and, optionally, organic binders, lubricants, compaction aids, etc.) may be injected into a mold cavity having a shape corresponding to a desirable shape for a non-integral tooth 111 to form a green body. The green body then may be removed from the mold and sintered to a desired final density in a furnace to form the non-integral tooth 111.

By way of example and not limitation, the non-integral tooth 111 may be attached to the cone body 108 by bonding (e.g., brazing or welding) the non-integral tooth 111 to the cone body 108 with a metallic material. The metallic material 154 may comprise, for example, an iron-based alloy, a nickel-based alloy, or a cobalt-based alloy. FIG. 10 is a partial cross-sectional view of a non-integral tooth 111 attached to a cone body 108 between two integral teeth 110. As shown in FIG. 10, a metallic material 154 may be disposed between at least a portion of the non-integral tooth 111 and the cone body 108. FIG. 11 is a partial perspective view of a non-integral tooth 111 welded to a cone body 108 with a bead of metallic material 154 adjacent an integral tooth 110. The bead of metallic material 154 may be welded to the non-integral tooth 111 and the cone body 108 around the perimeter of the base of the non-integral tooth 111.

Separately fabricating a non-integral tooth 111 and subsequently attaching the non-integral tooth 111 to the cone body 108 may be relatively useful for smaller cone bodies 108 on which it may be difficult to form a non-integral tooth 111 directly on the cone body 108, as previously described herein.

In additional embodiments, the non-integral tooth 111 and the cone body 108 may be co-sintered together in a furnace to bond the non-integral tooth 111 to the cone body 108.

Although the previously described embodiments of the present invention include a roller cone 109 having both integral teeth 110 and non-integral teeth 111, additional embodiments of the present invention include roller cones having all non-integral teeth 111 and no integral teeth 110. Such non-integral teeth 111 may be formed directly on the cone body 108, or separately formed and attached to the cone body 108 as previously described herein.

Additional embodiments of the present invention may comprise cutting structures other than teeth. For example, FIG. 12 illustrates an example embodiment of a roller cone 177 of the present invention having disk cutters. The roller cone 177 has an outer disk cutter 183, an inner disk cutter 184, and an intermediate disk cutter 186. Each of the disk cutters 183, 184, 186 extends circumferentially around the cone body 108 about a rotational axis thereof. In additional embodiments, the roller cone 177 may comprise more or fewer disk cutters. One or more of the disk cutters 183, 184, 186 may be an integral disk cutter that is integrally formed with and an integral part of the cone body 108. Additionally, one or more of the disk cutters 183, 184, 186 may comprise a non-integral disk cutter that is formed on the cone body 108 or formed separately from the cone body 108 and attached thereto.

One example of an embodiment of a method of the present invention that may be used to form a cone, such as the roller cone 177 shown in FIG. 12, is described below with reference to FIG. 13. As shown in FIG. 13, a cone body 108 may be shaped (e.g., machined) to form an intermediate cone structure 178 comprising an integral disk cutter 183, another integral disk cutter 184, and a gap or recess 132 between the integral disk cutter 183 and the integral disk cutter 184.

A layer of hardfacing material 120 may be applied to the integral disk cutter 183 and the integral disk cutter 184 using techniques known in the art as previously described. After applying hardfacing material 120 to the integral disk cutter 183 and the integral disk cutter 184, the non-integral disk cutter 186 may be formed directly on the cone body 108, or the non-integral disk cutter 186 may be separately formed from the cone body 108 and subsequently attached thereto to form the roller cone 177 shown in FIG. 12.

The non-integral disk cutter 186 may be provided on the cone body 108 in the at least one gap 132 by, for example, depositing hardfacing material 120 over a surface of the cone body 108 in the at least one gap 132 and forming the at least one non-integral disk cutter 186 from the hardfacing material 120.

FIG. 14 is an enlarged perspective view of another embodiment of a roller cone 195 of the present invention. The roller cone 195 is similar to the roller cone 177 shown in FIG. 12 and includes a cone body 108, an outer integral disk cutter 192, an inner integral disk cutter 194, and an intermediate non-integral disk cutter 196. In the embodiment of FIG. 14, however, the disk cutters 192, 194, 196 have a serrated cutting edge. The roller cone 195 shown in FIG. 14 may be formed using embodiments of methods of the present invention, as previously described herein.

While the present invention is described herein in relation to embodiments of earth-boring rotary drill bits that include rolling cutters and to embodiments of methods for forming such drill bits, the present invention also encompasses other types of earth-boring tools such as, for example, reamers, mills, and so-called “hybrid bits” that include both one or more roller cones and fixed cutters on blades or other supporting structures, as well as methods for forming such tools. Thus, as employed herein, the term “drill bit” includes and encompasses all of the foregoing earth-boring tools, as well as components and subcomponents of such structures.

While the present invention has been described herein with respect to certain embodiments, those of ordinary skill in the art will recognize and appreciate that it is not so limited. Rather, many additions, deletions and modifications to the embodiments described herein may be made without departing from the scope of the invention as hereinafter claimed. In addition, features from one embodiment may be combined with features of another embodiment while still being encompassed within the scope of the invention as contemplated by the inventor. 

1. A method of forming a roller cone for an earth-boring rotary drill bit, comprising: forming at least two integral teeth on a cone body with at least one gap therebetween; and providing at least one non-integral tooth on the cone body in the at least one gap.
 2. The method of claim 1, further comprising applying a hardfacing material to at least one surface of each tooth of the at least two integral teeth.
 3. The method of claim 1, wherein forming the at least two integral teeth on the cone body comprises: forming a first row of integral teeth extending circumferentially about a rotational axis of the cone body; and forming a second row of integral teeth extending circumferentially about a rotational axis of the cone body; and wherein the at least one gap comprises at least one gap between a tooth of the first row of integral teeth and a tooth of the second row of integral teeth.
 4. The method of claim 1, wherein forming the at least two integral teeth on the cone body comprises forming at least one row of integral teeth extending circumferentially about a rotational axis of the cone body, and wherein the at least one gap between the at least two integral teeth comprises at least one gap between two teeth of the at least one row of integral teeth.
 5. The method of claim 1, wherein providing the at least one non-integral tooth on the cone body in the at least one gap comprises providing two or more non-integral teeth on the cone body in the at least one gap.
 6. The method of claim 1, further comprising: marking an area on a surface of the cone body in the at least one gap; and providing the at least one non-integral tooth on the marked area on the surface of the cone body in the at least one gap.
 7. The method of claim 6, wherein marking an area on the surface of the cone body comprises forming a stub on the cone body in the at least one gap, and wherein forming the at least one non-integral tooth comprises forming the at least one non-integral tooth on the stub.
 8. The method of claim 1, wherein forming the at least one non-integral tooth on the cone body in the at least one gap comprises: successively depositing multiple layers of hardfacing material over the cone body in the at least one gap; and forming the at least one non-integral tooth from the multiple layers of hardfacing material.
 9. The method of claim 8, further comprising robotically manipulating the cone body while using a welding torch to deposit the multiple layers of hardfacing material.
 10. The method of claim 9, further comprising: using the welding torch to generate a plasma-transferred arc; and pulsing a current of the plasma-transferred arc as the welding torch is used to deposit the multiple layers of hardfacing material.
 11. The method of claim 7, wherein successively depositing the multiple layers of hardfacing material comprises: forming an interior region of the at least one non-integral tooth from a first hardfacing composition; and forming an exterior region of the at least one non-integral tooth from a second hardfacing composition differing from the first hardfacing composition.
 12. The method of claim 7, further comprising removing at least a portion of the hardfacing material from the at least one non-integral tooth to provide the at least one non-integral tooth with a desired shape.
 13. The method of claim 12, further comprising placing a template over the at least one non-integral tooth and machining the at least one non-integral tooth to conform to the template.
 14. The method of claim 1, wherein providing at least one non-integral tooth on the cone body in the at least one gap comprises: forming the at least one non-integral tooth separately from the cone body; and attaching the at least one non-integral tooth to the cone body.
 15. The method of claim 14, wherein forming the at least one non-integral tooth comprises: injecting a powder mixture comprising hard particles and particles of a metal-matrix material into a mold cavity to form a green body; and sintering the green body to a desired final density to form the at least one non-integral tooth.
 16. The method of claim 14, wherein attaching the at least one non-integral tooth to the cone body comprises bonding the at least one non-integral tooth to the cone body with a metallic material.
 17. The method of claim 16, wherein bonding the at least one non-integral tooth to the cone body with the metallic material comprises: providing the metallic material between the at least one non-integral tooth and the cone body; and co-sintering the at least one non-integral tooth, the cone body, and the metallic material.
 18. A method of forming a roller cone for an earth-boring rotary drill bit, comprising: forming at least two integral disk cutters on a cone body to extend circumferentially on the cone body about a rotational axis of the cone body; leaving at least one gap between the at least two integral disk cutters; and providing at least one non-integral disk cutter on the cone body in the at least one gap.
 19. The method of claim 18, wherein providing the at least one non-integral disk cutter on the cone body in the at least one gap comprises: depositing hardfacing material over a surface of the cone body in the at least one gap; and forming the at least one non-integral disk cutter from the hardfacing material.
 20. The method of claim 18, further comprising forming a serrated edge on the at least one non-integral disk cutter.
 21. The method of claim 20, wherein building up the at least one non-integral tooth in the gap comprises successively depositing layers of the hardfacing material in the gap using a welding torch.
 22. A method of forming a roller cone for an earth-boring rotary drill bit, comprising: forming at least one integral disk cutter on a cone body to extend circumferentially on the cone body about a rotational axis of the cone body; and providing at least one non-integral disk cutter on the cone body.
 23. A method of forming an earth-boring bit, the method comprising: forming a plurality of integral teeth on at least one cutter; forming a gap between at least two adjacent integral teeth of the plurality of integral teeth; applying a hardfacing layer to at least one surface on each of the at least two adjacent integral teeth of the plurality of integral teeth; and depositing hardfacing material in the gap between the at least two adjacent integral teeth and building up at least one non-integral tooth in the gap using the deposited hardfacing material.
 24. A method of forming an earth-boring bit, the method comprising: forming a plurality of integral teeth on at least one cutter; providing a gap between at least two adjacent integral teeth of the plurality of integral teeth; applying a hardfacing layer to at least one surface on each of the at least two adjacent integral teeth of the plurality of integral teeth; forming at least one non-integral tooth separately from the at least one cutter, comprising: molding a green body comprising a plurality of hard particles and a plurality of particles comprising a metallic matrix material; and sintering the green body to form the non-integral tooth; and bonding the at least one non-integral tooth to the at least one cutter in the gap between the at least two adjacent integral teeth with a metallic binder material.
 25. An earth-boring bit, comprising: a body having at least one bit leg; a roller cone mounted to the at least one bit leg and rotatable on the at least one bit leg about a rotational axis; at least one integral tooth formed on a surface of the roller cone; a hardfacing material deposited on at least one surface of the at least one integral tooth; at least one non-integral tooth bonded to the surface of the roller cone adjacent to the at least one integral tooth, the at least one non-integral tooth comprising a particle-matrix composite material.
 26. The earth-boring bit of claim 25, wherein the at least one non-integral tooth comprises an interior region having a first hardfacing composition and an exterior region having a second hardfacing composition, the first hardfacing composition exhibiting a toughness greater than a toughness exhibited by the second hardfacing composition, and the second hardfacing composition exhibiting a wear resistance greater than a wear resistance exhibited by the first hardfacing composition.
 27. The earth-boring bit of claim 25, wherein the at least one non-integral tooth comprises multiple layers of hardfacing material. 